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Temperature Cross Heat Exchanger

heat exchanger temperature cross

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#1 Priolo


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Posted 12 August 2019 - 12:46 PM



I would like to ask if a temperature cross (Hot outlet - Cold Outlet < 0 ) is possible to reach in a TEMA Type Heat Exchangers with 2 tube passes. 

Let's imagine to have  a BEU TEMA Type exchanger (2 tube passes, 1 shell pass) where in both shell and tubes we have hydrocarbons.

If for the design case (highest duty and highest flowrate) we have considered a temperature approach Hot Outlet - Cold Outlet = 0, at reduced duty and flowrate (both on tube and shell side) it's possible to have temperature cross (Hot outlet - Cold Outlet < 0 )?

I've simulated with PRO/II the two scenarios (design and reduced flowrate) and, keeping for both the UA calculated in the design case, I got a temperature cross for the reduced flowrate case. Is this possible? Lot of forums say that temperature cross is not possible in multipass heat exchangers.


Thank you.



#2 PhilippM


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Posted 12 August 2019 - 01:54 PM

I don't see why a temperature cross couldn't occur in this configuration. For the sake of argument let's say your hot medium is on the shell side and the cold one on the tubeside. Near the shell side outlet the hot medium can be cooled down so far that it is colder than the cold medium at its outlet, therefore causing a temperature cross.

#3 IGC


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Posted 13 August 2019 - 04:40 AM

You would need to do a more detailed check on the heat exchanger by splitting it into zones depending on what type of baffling you have for the tube bundle.  




This previous post and the excel spreadsheet there goes into it in detail, but yes it is possible to have a temperature cross in a BEU unit.  For example a LIN vaporiser could be something like, tubeside:  -196 degC in / +30 degC out.  Shellside:  +50 degC in / 20 degC out.  There is a cross when you look at just the inlet and outlet temperatures but internally it is a bit more complicated.

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